Carbon-substitution effect on the electronic properties ofMgB2single crystals

Abstract

The electronic properties of the carbon substituted MgB2 single crystals are reported. The carbon substitution drops Tc below 2 K. In-plane resistivity shows a remarkable increase in residual resistivity by C-substitution, while the change of in-plane/out-of-plane Hall coefficients is rather small. Raman scattering spectra indicate that the E2g-phonon frequency radically hardens with increasing the carbon-content, suggesting the weakening of electron-phonon coupling. Another striking C-effect is the increases of the second critical fields in both in-plane and out-of-plane directions, accompanied by a reduction in the anisotropy ratio. The possible changes in the electronic state and the origin of Tc-suppression by C-substitution are discussed.

Effect of damage by 2 MeV He ions and annealing on Hc2 in MgB2 thin films

“…The fact that there is no correlation of H c2 (0) with ρ across numerous samples leads to the suggestion that the measured resistivity is ρ π , while H c2 (0) is determined by σ-band scattering 15 (ρ σ ), with the magnitude of ρ σ being 125 to 165 µΩ cm. 6 However, to explain the observed form of H c2 (T), 16 and of irradiation, 14 and alloying with carbon, 4 is similar to that seen in many A15 and ternary boride superconductors, 17 it is not necessary to invoke interband scattering to explain such a reduction in T c . Smearing of the peak, and reduction of the density of states at the …”

“…Of particular interest is the large increase in H c2 that results from alloying with carbon, [1][2][3][4] and also, in the case of thin films, from disorder and possibly impurities that are introduced during deposition. 5 It has been shown that in Three MgB 2 thin films (A, S, and PB), all grown on sapphire substrates, were used for this study, while PA was used earlier.…”

Influence of the upper critical-field anisotropy on the transport properties of polycrystalline MgB2

“…A reduction of γ was reported after neutron irradiation [23,24] or can be achieved by carbon doping [30], but it seems to be always accompanied by an increase of the upper critical field B c2 (which further enhances B ⊥ c2 and enlarges the application range). Although experimentally difficult, the influence of such a "pure" change of anisotropy on J c is demonstrated in Fig.…”

Enhancement of flux pinning and high critical current density in graphite doped MgB2 superconductor

“…Reduction of coherence length due to enhanced impurity scattering is considered to contribute to the enhancement of H c2 [30][31][32][33] . Furthermore, flux pinning strength was found to be enhanced by carbon substitution 6,19,20,23,24 .…”